ContinentalContinental Drift Theory Drift Theory

ContinentalContinental Drift Theory Drift Theory

• Proposed by Alfred Wegener in 1912

• 250 million years ago, all of the continents were combined into one super-continent called “Pangaea”

• The continents gradually drifted apart to where they are today

““PuzzlePuzzle Pieces”Pieces”

• Continents look like they could be part of a giant jigsaw puzzle

Distribution of FossilsDistribution of Fossils

• Plant and animal fossils found on the coastlines of different continents

Ancient ClimatesAncient Climates

• Tropical plant remains (coal deposits) found in Antarctica

• Glaciation in Africa, South America, India, and Australia during the same time

Sequence of RocksSequence of Rocks

• Same rock patterns found in South America, India, Africa, Antarctica and Australia

Problems With The TheoryProblems With The Theory

• Theory was not accepted by scientists…why?– Because Wegner could not identify the

cause of continental drift

Causes of Plate Causes of Plate Tectonics/DriftingTectonics/Drifting

Convection CurrentsConvection Currents

• Hot magma in the Earth moves toward the surface, cools, then sinks again.

• Creates convection currents beneath the plates that cause the plates to move.

Heat Transfer.mht

Heat Transfer The Driving Force of Plate Tectonics

Theory of Plate TectonicsTheory of Plate Tectonics

Plate TectonicsPlate Tectonics

Plate BoundariesPlate Boundaries

Causes of Plate TectonicsCauses of Plate Tectonics

Plate TectonicsPlate Tectonics

What is Plate TectonicsWhat is Plate Tectonics

• The Earth’s crust and upper mantle are broken into sections called plates

• Plates move around on top of the mantle like rafts

What is the What is the LithosphereLithosphere??

• The crust and part of the upper mantle = lithosphere–100 km thick

–Less dense than the material below it so it “floats”

What is the What is the AsthenoshereAsthenoshere??

• The plastisity layer below the lithosphere = asthenosphere

• The plates of the lithosphere float on the asthenosphere

2 Types of Plates2 Types of Plates

• Ocean plates - plates below the oceans

• Continental plates - plates below the continents

Plate BoundariesPlate Boundaries

Divergent BoundariesDivergent Boundaries

• Boundary between two plates that are moving apart or rifting

• RIFTING causes SEAFLOOR

SPREADING

Divergent Boundaries Divergent Boundaries create…create…

• Mid-ocean ridges

• rift valleys

• fissure volcanoes

Convergent BoundariesConvergent Boundaries

• Boundaries between two plates that are colliding

• There are 3 types…

Type 1Type 1• Ocean plate colliding with a

less dense continental plate• Subduction Zone: where the

more dense plate slides under the less dense plate

• VOLCANOES occur at subduction zones

Andes Mountains, Andes Mountains, South AmericaSouth America

Type 2Type 2

• Ocean plate colliding with another ocean plate

• The more dense plate slides under the less dense plate creating a subduction zone called a TRENCH

Aleutian Islands, AlaskaAleutian Islands, Alaska

Type 3Type 3

• A continental plate colliding with another continental plate

• Have Collision Zones:–a place where folded and thrust

faulted mountains form.

Transform Fault BoundariesTransform Fault Boundaries

• Boundary between two plates that are sliding past each other

• EARTHQUAKES along faults• Another example of a transform

boundary is the San Andres Fault

San Andreas Fault, CASan Andreas Fault, CA

Sea-Floor Spreading

Introduction

• Tube Worms - live in the Pacific Ocean about one mile deep near the hydrothermal vents.

Mapping the mid-ocean ridge

• The East Pacific Rise has a mid-ocean ridge.

• Curves around like a baseball.

• Lies hidden under hundreds of meters of water.

Sonar

• A device that bounces sound waves off underwater objects and then records the echoes of these sound waves.

• Sonar mapped mid-ocean ridges.

Harry Hess

• An American geologist who studied mid-ocean ridges.

• He suggested that the ocean floors move like conveyor belts, carrying the continents along with them.

• At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge. As the molten material cools, it forms a strip of solid rock in the center of the ridge. Then more molten material flows into the crack.

Sea-floor spreading

• The process that continually adds new material to the ocean floor.

• Evidence molten material, magnetic stripes, and drilling samples.

Evidence• Magnetic Stripes.

How does the pattern of matching stripes show evidence of sea-floor spreading?

Evidence #3 - Drilling Samples

• The Glomar Challenger did a drilling sample and found rocks that the farther away from the ridge the older the rocks were. The younger ones were in the center of the ridge.